Photogravitationally Restricted Three-Body Problem and Coplanar Libration Point

The photogravitationally restricted three-body problem in which the mass reduction factors of two primaries q₁, q₂ ∈ (-∞,1 is studied and the calculating formula of the location of coplanar libration points is given in this paper. As an application, the motion of cometary dust in the solar system and dust grain in binary AR Cas is also discussed.